Method of forming thick layer by screen printing and method of forming piezoelectric actuator of inkjet head

ABSTRACT

A method to form a thick layer by screen printing and a method to form a piezoelectric actuator of an inkjet head. The method to form the thick layer including forming a guide groove in a surface to a predetermined depth, and forming the thick layer by applying a material to the surface inside the guide groove through screen printing. The method to form the piezoelectric actuator including forming an insulating layer on a top surface of a vibration plate and forming a guide groove in the top surface of the vibration plate or an insulating layer to a predetermined depth at a position corresponding to each of a plurality of pressure chambers, forming a lower electrode on the top surface of the insulating layer; forming a piezoelectric layer inside the guide groove by screen printing, and forming an upper electrode on a top surface of the piezoelectric layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.11/581,334, filed Oct. 17, 2006, in the U.S. Patent and TrademarkOffice, which claims the benefit under 35 U.S.C. §119 of Korean PatentApplication No. 10-2006-15628, filed on Feb. 17, 2006, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present general inventive concept relates to a method of forming athick layer more uniformly by screen printing, and a method of forming apiezoelectric actuator of an inkjet head using the method of forming thethick layer.

2. Description of the Related Art

Inkjet heads are devices for printing an image on a printing medium byejecting ink droplets onto a desired region of the printing medium.Depending on an ink ejecting method, the inkjet heads can be classifiedinto two types: thermal inkjet heads and piezoelectric inkjet heads. Athermal inkjet head generates bubbles in an ink to be ejected by usingheat and ejects the ink utilizing an expansion of the bubbles, and apiezoelectric inkjet head ejects an ink using a pressure generated bydeforming a piezoelectric material.

FIG. 1A is a sectional view illustrating a conventional piezoelectricinkjet head, and FIG. 1B illustrates a sectional view taken along lineA-A′ of FIG. 1A. The conventional piezoelectric inkjet head illustratedin FIGS. 1A and 1B is formed by a conventional screen printing method.

Referring to FIGS. 1A and 1B, a manifold 11, a plurality of restrictors12, and a plurality of pressure chambers 13 forming an ink flow channelare formed in a flow channel plate 10 of the conventional piezoelectricinkjet head. A vibration plate 20, which can be deformed bypiezoelectric actuators 40, is bonded to a top surface of the flowchannel plate 10, and a nozzle plate 30 in which a plurality of nozzles31 are formed is bonded to a bottom surface of the flow channel plate10. The vibration plate 20 can be formed integrally with the flowchannel plate 10, and the nozzle plate 30 can also be formed integrallywith the flow channel plate 10.

The manifold 11 is an ink passage for supplying ink from an inkreservoir (not illustrated) to the respective pressure chambers 13, andthe restrictors 12 are ink passages allowing inflow of ink from themanifold 11 to the pressure chambers 13. The pressure chambers 13 arefilled with and eject the supplied ink and are arranged at one side orboth sides of the manifold 11. The nozzles 31 are formed through thenozzle plate 30 and are connected to the respective pressure chambers13. The vibration plate 20 is bonded to the top surface of the flowchannel plate 10 to cover the pressure chambers 13. The vibration plate20 is deformed by the operation of the piezoelectric actuators 40. Thus,pressures in the respective pressure chambers 13 change and the ink isejected from the pressure chambers 13 by the operation of thepiezoelectric actuators 40. Each of the piezoelectric actuators 40includes a lower electrode 41, a piezoelectric layer 42, and an upperelectrode 43 that are sequentially stacked on the vibration plate 20.The lower electrode 41 is formed on the entire surface of the vibrationplate 20 as a common electrode. The piezoelectric layer 42 is formed onthe lower electrode 41 above each of the pressure chambers 13. The upperelectrode 43 is formed on the piezoelectric layer 42 as a drivingelectrode for applying a voltage to the piezoelectric layer 42.

In the conventional piezoelectric inkjet head, the piezoelectricactuator 40 is usually formed as follows. The lower electrode 41 isformed by sputtering a metal to a predetermined thickness on a topsurface of the vibration plate 20. The piezoelectric layer 42 is formedby applying a piezoelectric ceramic material paste to a predeterminedthickness to a top surface of the lower electrode 41 through screenprinting, and by sintering the applied piezoelectric ceramic materialpaste. The upper electrode 43 is formed by applying a conductivematerial to a top surface of the piezoelectric layer 42 by screenprinting and sintering the applied conductive material.

When forming the piezoelectric layer 42, the piezoelectric ceramicmaterial paste is applied to the lower electrode 41 to a thickness ofseveral tens of micrometers, and then the piezoelectric ceramic materialpaste is dried and sintered to obtain a thick layer for thepiezoelectric layer 42. However, since the piezoelectric ceramicmaterial paste applied to the lower electrode 41 is thick, thepiezoelectric ceramic material paste spreads outward with time. Thismakes the piezoelectric layer 42 relatively thicker at a center portionand thinner at edge portions as illustrated in FIG. 1B, such that athickness and a width of the piezoelectric layer 42 are not uniform.Further, an outer edge of the piezoelectric layer 42 can be curvedalthough a straight outer edge is preferable. Accordingly, the overallshape of the piezoelectric layer 42 can be irregularly curved.

Furthermore, due to the unevenness of the piezoelectric layer 42, thethickness and the width of the upper electrode 43 formed on thepiezoelectric layer 42 may not be uniform. In addition, the distancebetween the lower electrode 41 and the upper electrode 43 is notconstant because of the uneven thickness of the piezoelectric layer 42,and thus an electric field cannot be uniformly formed between the lowerelectrode 41 and the upper electrode 43.

Additionally, nozzle density should be high to realize high-qualityprinting such as high-resolution and high-speed printing. The nozzledensity is usually denoted using “cpi (channel per inch),” and theresolution of an image is usually denoted using “dpi (dot per inch).” Toincrease the nozzle density, the distance between adjacent pressurechambers 13 should be reduced. Accordingly, the distance betweenadjacent piezoelectric layers 42 should be reduced. However, asdescribed above, since the piezoelectric layer 42 formed by aconventional method has an uneven width, the piezoelectric layer 42 mayeasily make contact with an adjacent piezoelectric layer 42 when theyare formed closer to each other, making it difficult to increase thenozzle density much more.

As mentioned above, in the conventional method of forming a thick layerby screen printing, the thickness and width of the piezoelectric layer42 of the piezoelectric actuator 40 cannot be uniformly formed. Further,the conventional method makes it difficult to increase the nozzledensity of the inkjet head.

SUMMARY OF THE INVENTION

The present general inventive concept provides a method of forming athick layer by screen printing and a method of forming a piezoelectricactuator of an inkjet head using the method of forming the thick layer.The method allows a piezoelectric layer to have a uniform width andthickness, and also allows the nozzle density of the inkjet head to beincreased.

Additional aspects and advantages of the present general inventiveconcept will be set forth in part in the description which follows and,in part, will be obvious from the description, or may be learned bypractice of the general inventive concept.

The foregoing and/or other aspects and utilities of the present generalinventive concept may be achieved by providing a method of forming athick layer on a surface by screen printing, the method includingforming a guide groove in the surface to a predetermined depth, andapplying a paste material inside the guide groove formed on the surfacethrough screen printing.

The guide groove may have the same contour as a desired contour of thethick layer.

A width of the material applied to the inside of the guide groove may besmaller than the width of the guide groove such that, the paste materialis allowed to spread laterally inside the guide groove and the pastematerial has a width corresponding to the width of the guide groove anda uniform thickness.

The amount of the paste material applied to the inside of the guidegroove may be such that a thick layer of the paste material has auniform thickness.

A thick layer formed of the paste material may have a thickness of aboutseveral tens of micrometers.

The foregoing and/or other aspects and utilities of the present generalinventive concept may also be achieved by providing a method of forminga piezoelectric actuator on a vibration plate of an inkjet head, themethod including forming an insulating layer on a top surface of thevibration plate, forming a guide groove at a top surface of thevibration plate or the insulating layer to a predetermined depth at aposition corresponding to a pressure chamber of the inkjet head, forminga lower electrode on the top surface of the insulating layer, applying apiezoelectric material to a top surface of the lower electrode insidethe guide groove by screen printing to form a piezoelectric layer, andforming an upper electrode on a top surface of the piezoelectric layer.

The piezoelectric material may be a paste.

The guide groove may be formed at the top surface of the vibrationplate, and then the insulating layer may be formed on the top surface ofthe vibration plate.

The insulating layer may be formed on the top surface of the vibrationplate, and then the guide groove may be formed at the top surface of theinsulating layer.

The insulating layer may be a silicon oxide layer.

The forming of the lower electrode may include depositing a conductivemetal on the top surface of the insulating layer to a predeterminedthickness.

The forming of the lower electrode may include sequentially depositing aTi later and a Pt layer through sputtering.

The guide groove may have the same contour as a desired contour of thepiezoelectric layer.

The forming of the guide groove may include forming a guide groovehaving a same contour as a desired contour of the piezoelectric layerafter the lower electrode is formed at the top surface of the insulatinglayer.

The guide groove may have a width corresponding to the width of thepressure chamber.

The applying of the piezoelectric material may include applying thepiezoelectric material paste inside the guide groove in such a mannerthat the width of the piezoelectric material paste applied is smallerthan the width of the guide groove.

The applying of the piezoelectric material paste may further includeallowing the piezoelectric material paste applied inside the guidegroove to spread laterally to have a width corresponding to the width ofthe guide groove.

The applying of the piezoelectric material paste may further includeallowing the piezoelectric material paste applied inside the guidegroove to spread laterally to have a uniform thickness, a uniform width,and a straightened vertical outer edge.

The forming of the upper electrode may include applying an electrodematerial paste to the top surface of the piezoelectric layer by screenprinting.

The method may also include sintering the piezoelectric layer and theupper electrode.

The forming of the upper electrode may include depositing a conductivemetal on the top surface of the piezoelectric layer to a predeterminedthickness by sputtering.

The method may also include sintering the piezoelectric layer prior tothe forming of the upper electrode.

The foregoing and/or other aspects and utilities of the present generalinventive concept may also be achieved by providing a method of forminga piezoelectric actuator, the method including forming guide grooves ata first surface of a vibration plate, forming a lower electrode alongthe first surface of the vibration plate, including the guide grooves,applying a piezoelectric material to the lower electrode at the guidegrooves, and forming an upper electrode over the piezoelectric material.

The piezoelectric material may be a paste.

The applying of the piezoelectric material may include spreading thepiezoelectric material along an entire surface of the guide groove.

The applying of the piezoelectric material may include screen printingthe piezoelectric material to form a piezoelectric layer.

The method may further include forming an insulating layer over thefirst surface of the vibration plate before forming the lower electrodealong the first surface of the vibration plate.

The forming of the guide grooves at a first surface of the vibrationplate may include forming of guide grooves at a surface of theinsulating layer, and the forming of the lower electrode along the firstsurface of the vibration plate, including the guide grooves may includeforming a lower electrode along a top surface of the insulating layer,including the guide grooves.

The foregoing and/or other aspects and utilities of the present generalinventive concept may also be achieved by providing a piezoelectricinkjet head including a flow channel plate having a plurality ofpressure chambers, a vibration plate bonded to a top surface of the flowchannel plate to cover the pressure chambers, an insulating layer formedon a top surface of the vibration plate, a nozzle plate having aplurality of nozzles corresponding to the pressure chambers, bonded to abottom surface of the flow channel plate, and a plurality ofpiezoelectric actuators bonded to a top surface of the insulating layerto provide ink-ejecting forces to the respective pressure chambers bydeforming the vibration plate, wherein a top surface of the insulatinglayer or a top surface of the vibration plate has a plurality of guidegrooves of a predetermined depth and width, and the plurality of guidegrooves are disposed in positions corresponding to the plurality ofpressure chambers.

The top surface of the vibration plate may have the plurality of guidegrooves.

The top surface of the insulating layer vibration plate may have theplurality of guide grooves.

The plurality of piezoelectric actuators may include a lower electrodeformed on a top surface of the insulating layer as a common electrode, aplurality of piezoelectric layers formed inside each of the plurality ofguide grooves on a top surface of the lower electrode, and a pluralityof upper electrodes, each formed on a top surface of the plurality ofpiezoelectric layers as driving electrodes.

The piezoelectric layer may have a uniform width, a uniform thickness,and a straightened vertical outer edge.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the present generalinventive concept will become apparent and more readily appreciated fromthe following description of the embodiments, taken in conjunction withthe accompanying drawings of which:

FIG. 1A is a sectional view illustrating a conventional piezoelectricinkjet head, and FIG. 1B illustrates a sectional view taken along lineA-A′ of FIG. 1A;

FIGS. 2A through 2E illustrate a method of forming a piezoelectricactuator of an inkjet head using a method of forming a thick layer byscreen printing according to an embodiment of the present generalinventive concept; and

FIGS. 3A through 3C illustrate a method of forming a piezoelectricactuator of an inkjet head using a method of forming a thick layer byscreen printing according to another embodiment of the present generalinventive concept.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentgeneral inventive concept, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to the likeelements throughout. The embodiments are described below in order toexplain the present general inventive concept by referring to thefigures.

FIGS. 2A through 2E illustrate a method of forming a piezoelectricactuator of an inkjet head using a method of forming a thick layer byscreen printing according to an embodiment of the present generalinventive concept.

Referring to FIG. 2A, the piezoelectric inkjet head may include aplurality of plates forming an ink flow channel. For example, threeplates may be used: a flow channel plate 110, a vibration plate 120, anda nozzle plate 130. A manifold (not illustrated), a plurality ofrestrictors (not illustrated), and a plurality of pressure chambers 113may be formed in the flow channel plate 110, and the vibration plate 120may be bonded to a top surface of the flow channel plate 110 to coverthe pressure chambers 113. The nozzle plate 130 may be bonded to abottom surface of the flow channel plate 110. A plurality of nozzles 131are formed through the nozzle plate 130 corresponding to the pressurechambers 113. The flow channel plate 110 may be formed with a manifold(not illustrated) and a plurality of restrictors (not illustrated).Meanwhile, the vibration plate 120 can be formed integrally with theflow channel plate 110, and the nozzle plate 130 can also be formedintegrally with the flow channel plate 110.

A plurality of piezoelectric actuators 140 provide ink-ejecting forcesto the respective pressure chambers 113 by deforming the vibration plate120 (refer to FIG. 2E). The plurality of piezoelectric actuators 140 canbe formed on the vibration plate 120 through the following operations.

Referring again to FIG. 2A, an insulating layer 121 is formed on theentire top surface of the vibration plate 120. The insulating layer 121can have a thickness of about 1 μm to about 2 μm. When the vibrationplate 120 is formed of silicon, the insulating layer 121 may be formedof a silicon oxide.

Referring to FIG. 2B, a plurality of guide grooves 125 are formed in atop surface of the insulating layer 121 to a predetermined depth. Theguide grooves 125 may be formed by partially removing the insulatinglayer 121 through a removal method such as etching, using a patternedphotoresist as an etch mask. For example, when the insulating layer 121has a thickness of about 1 μm to about 2 μm as described above, theguide grooves 125 can have a depth approximately equal to half thethickness of the insulation layer 121 (i.e., about 0.5 μm to about 1μm). The guide grooves 125 are formed in the insulating layer 121 atlocations corresponding to the respective pressure chambers 113. Theguide grooves 125 may be formed to have the same contour as a desiredcontour of the piezoelectric layers 142 (refer to FIG. 2D) of thepiezoelectric actuators 140, or may be formed to have the same contouras a desired contour of the piezoelectric layer 142 taking intoconsideration the formation of the lower electrode 141, as describedbelow. The width of the guide grooves 125 may be substantially the sameas that of the pressure chambers 113.

Referring to FIG. 2C, the lower electrode 141 is formed on theinsulating layer 121 as a common electrode. The lower electrode 141 maybe formed by depositing a conductive metal on an entire top surface ofthe insulating layer 121 to a predetermined thickness. Although thelower electrode 141 can be formed of a single metal layer, the lowerelectrode 141 may also be formed of two metal layers such as Ti and Ptlayers. For example, the Ti metal layer can be formed to a thickness ofabout 400 Å by sputtering, and the Pt metal layer can be formed to athickness of about 5000 Å by sputtering.

Referring to FIG. 2D, the piezoelectric layers 142 are formed on thelower electrode 141 inside the guide grooves 125. In detail, apiezoelectric material paste, such as a lead zirconate titanate (PZT)ceramic material paste, may be applied to the lower electrode to apredetermined thickness (e.g., about 30 μm to about 60 μm) by screenprinting. While a piezoelectric material paste may be used, the currentpresent general inventive concept is not limited thereto, and otherforms of piezoelectric material may be used which result in the intendedgeneral inventive concept. The piezoelectric material paste may beapplied in such a manner that a width of the piezoelectric layers 142 isslightly smaller than that of the guide grooves 125. Since the appliedpiezoelectric material paste may laterally spread with time, thepiezoelectric layers 142 are leveled and widened into a more uniformshape as illustrated in FIG. 2D. The width of the piezoelectric layers142 is restricted by the width of the grooves 125, such that the widthof the piezoelectric layers 142 can be uniform. Further, a thickness ofthe piezoelectric layers 142 can be relatively uniform when comparedwith the related art. The piezoelectric layers 142 may be driednaturally or dried forcibly by using a hot plate heated up to about 100°C. Other suitable drying methods can be selected depending oncharacteristics of the piezoelectric material paste applied, such as aviscosity of the piezoelectric material paste.

Referring to FIG. 2E, upper electrodes 143 are formed on the respectivepiezoelectric layers 142 as driving electrodes. The upper electrodes 143may be formed by applying an electrode material, paste, such as an Ag—Pdpaste, to top surfaces of the piezoelectric layers 142 by screenprinting and drying the applied electrode material paste. Then, thepiezoelectric layers 142 and the upper electrodes 143 may be sintered ata temperature of about 900° C.˜1200° C. After that, the piezoelectriclayers 142 may shrink to a thickness of about 10 μm to about 30 μm.

As illustrated in FIG. 2E, after the above-described operations thepiezoelectric actuators 140 can have a sequentially stacked structureformed by the lower electrode 141, the piezoelectric layers 142, and theupper electrodes 143. The piezoelectric layers 142 of the piezoelectricactuators 140 can have a relatively uniform width and thickness, andouter vertical edges of the piezoelectric actuators can be straightenedowing to the guide grooves 125.

While the upper electrodes 143 can be formed by screen printing asdescribed above, the present general inventive concept is not limitedthereto and the upper electrodes 143 can also be formed by sputtering.For example, the piezoelectric layers 142 may be sintered before theupper electrode layers 143 are formed. Then, an electrode material, suchas a conductive metal like Au or Pt, is deposited on the piezoelectriclayers 142 to a predetermined thickness by sputtering, thereby formingthe upper electrodes 143 as illustrated in FIG. 2E.

FIGS. 3A through 3C illustrate a method of forming a piezoelectricactuator of an inkjet head using a method of forming a thick layer byscreen printing according to another embodiment of the present generalinventive concept. The method illustrated in FIGS. 3A through 3C issimilar to the method illustrated in FIGS. 2A through 2E, except thatguide grooves are formed in a top surface of a vibration plate. Thus,the current embodiment will now be described briefly referencing similarprocesses illustrated in FIGS. 2A through 2E.

Referring to FIG. 3A, a plurality of guide grooves 126 are formed in atop surface of the vibration plate 120 to a predetermined depth. Theguide grooves 126 may be formed by partially removing the top surface ofthe vibration plate 120 through a removal method, such as etching, usinga patterned photoresist as an etch mask. Since the vibration plate 120may have a thickness of about 10 μm to about 20 μm, depending on thesize of pressure chambers 113, the vibration plate 120 is not affectedby the guide grooves 126 when a depth thereof is about 0.5 μm about 1μm. The guide grooves 126 are formed in the vibration plate 120 atlocations corresponding to the respective pressure chambers 113. Theguide grooves 126 may be formed to have the same contour as a desiredcontour of the piezoelectric layers 142 (refer to FIG. 3C) of thepiezoelectric actuators 140 or may be formed to have the same contour asa desired contour of the piezoelectric layer 142 taking intoconsideration the formation of an insulating layer 121 and a lowerelectrode 141, as described below. The width of the guide grooves 126may be substantially the same as that of the pressure chambers 113.

Referring to FIG. 3B, an insulating layer 121 and a lower electrode 141are sequentially formed on the entire top surface of the vibration plate120. The insulating layer 121 and the lower electrode 141 are formed inthe same way as for the embodiment illustrated in FIGS. 2A through 2E.

Referring to FIG. 3C, piezoelectric layers 142 are formed on the lowerelectrode 141 inside the guide grooves 126 by screen printing, and upperelectrodes 143 are formed on the piezoelectric layers 142 by screenprinting or sputtering. The piezoelectric layers 142 and the upperelectrodes 143 are formed in the same way as in the embodimentillustrated in FIGS. 2A through 2E.

As illustrated in FIG. 3C, after the above-described operations, thecomplete piezoelectric actuators 140 can have a sequentially stackedstructure formed by the lower electrode 141, the piezoelectric layers142, and the upper electrodes 143.

According to the present general inventive concept, a piezoelectriclayer of a piezoelectric actuator can be uniformly formed and a moreuniform electric field can be formed between the lower electrode and theupper electrode since the distance between the lower electrode and theupper electrode is more uniform. Further, the width of the piezoelectriclayer can be uniformly controlled, so that the nozzle density of theinkjet head can be easily increased.

Although a few embodiments of the present general inventive concept havebeen shown and described, it will be appreciated by those skilled in theart that changes may be made in these embodiments without departing fromthe principles and spirit of the general inventive concept, the scope ofwhich is defined in the appended claims and their equivalents.

1. A method of forming a thick layer on a surface by screen printing, the method comprising: forming a guide groove in the surface to a predetermined depth; and applying a paste material inside the guide groove formed on the surface through screen printing.
 2. The method of claim 1, wherein the guide groove has the same contour as a desired contour of the thick layer.
 3. The method of claim 1, wherein a width of the paste material applied to the inside of the guide groove is smaller than a width of the guide groove such that, the paste material is allowed to spread laterally inside the guide groove and the paste material has a width corresponding to the width of the guide groove and a uniform thickness.
 4. The method of claim 1, wherein an amount of the paste material applied to the inside of the guide groove is such that a thick layer of the paste material has a uniform thickness.
 5. The method of claim 1, wherein a thick layer formed of the paste material has a thickness of about several tens of micrometers. 